The field of the invention is suspension agents for synthetic resin powders and the invention is particularly concerned with suspension agents for synthetic resin powders used in the spot coating of interlinings for garments.
The state of the art of suspension agents useful for the preparation of printing pastes to be applied in spots to interlinings for garments may be ascertained by reference to Italian Pat. No. 301,283; West German Applications Nos. 2,007,971 Published Dec. 16, 1971 and 2,229,308 Published Jan. 3, 1974; and British Pat. No. 1,295,558, the disclosures of which are incorporated herein.
According to British Pat. No. 1,295,558 which corresponds to German Published Application No. 2,007,971, the spot coating of interlinings is carried out mainly by three methods:
1. A suitable plastic powder, for example, a polyamide or polyethylene based powder, is applied by a doctor blade to an engraving roller having recesses in the form of dots disposed in an even raster or grid formation and having a diameter of about 1 mm so that the plastic powder fills the recesses. The web of the interlining, which has been preheated to a high temperature by means of heating rollers, is passed around the engraving roller under tension and the plastics powder is transferred from the recesses to the web of interlining material.
2. A network of spots of a suitable plastics, such as polyethylene, is prepared in the form of a raster, the spots being interconnected by very fine webs. The network is applied dry to the hot interlining, the fine webs breaking up and disappearing, and the spots of the plastic fusing to the interlining. Interlinings of this kind have a relatively hard handle and can be fixed only on relatively heavy facing materials and the plastics also tend to bleed through and stick to the fixing press.
3. In the least expensive and least complex process, suitable plastics, such as PVC, polyamide or polyethylene, are mixed with plasticizers or in aqueous or solvent-containing media to form pastes which are printed by means of a printing roller formed with perforations arranged as a raster.
It is known to use aqueous solutions of the ammonium salts of polymeric organic acids as suspension agents and/or dispersants as disclosed in Italian Pat. No. 301,282. Improvements in the state of the art of these suspension agents are described in German Published Applications Nos. 2,007,971 and 2,229,308, and British Pat. No. 1,295,558. Preferably, the salts of the polymers or copolymers of acrylic acid are used. Dispersions prepared with the aid of these suspension agents, which are also called pastes, have, however, not been found to be fully satisfactory.
When these pastes are dried after the imprinting step, the suspension agents form a thin, but hard skin on the surface of the synthetic resin spots. When this phenomenon is not compensated for by the addition of suitable plasticizers, high heat sealing temperatures or pressures are required to attain satisfactory adhesion of the thus coated fabric to the covering materials. However, high concentrations of plasticizers, which prevent this troublesome effect, lead to poor stability of the bond with respect to super-heated steam, as is employed for example during steam ironing. Moreover, the structure of the interlining and the covering material has imparted thereto a rough handle due to the use of the salts of polymeric fatty acids and this indicates that a foreign substance has been incorporated between the actually soft fabrics and it is not necessary to be an expert to notice this.